1. Field of the Invention
The present invention relates to a process for preparing polymerization catalysts for olefins. Said catalysts are particularly suited for the polymerization of ethylene.
The present novel polymerization catalysts comprise a support consisting of an inorganic oxide or a mixture of inorganic oxides, the surface of said support having a Group IVa metal compound bound to its surface.
Furthermore, the present invention concerns a process for the homo- and copolymerization of olefins, in particular ethylene, in the presence of a heterogeneous catalyst.
2. Description of Related Art
It is known in the art that oligomerisation and polymerisation of ethylene can be catalysed by compositions comprising vanadium, titanium and/or zirconium halides and possibly other components on an inorganic oxidic support. Typically, these heterogeneous catalysts are prepared by stirring the support, for instance silica or alumina, in a solution of the transition metal compound(s) used, evaporating the product and, if desired, suspending it in a solution of a suitable cocatalyst compound, such as an organo-Al compound, before polymerization.
The prior art is hampered by considerable problems. For example, the use of solvents makes the processes complex because additional process steps (evaporation) are needed for separating the solvents from the products. Furthermore, as far as the preparation of Zr- and Hf-containing catalysts using chlorides is concerned, the reagents are solid substances, which are poorly soluble in non-polar solvents. Therefore, polar solvents, such as water and alcohols, will have to be used as reaction media. These solvents are, however, known to impair the activity of the catalysts.